Selective Solution in Planktonic Foraminifera: Liability and Asset in Reconstruction of Ancient Environments: ABSTRACT

Abstract

On the ocean floor, solution of foraminiferal ooze takes place at depths considerably above the CaCO3 compensation depth. Solution is selective and the common planktonic Foraminifera are dissolved in the following order (least resistant species listed first): Globigerinoides ruber, Orbulina universa, Globigerinella siphonifera, Globigerinoides sacculifer, G. conglobatus, Globigerina bulloides, Globigerinita glutinata, Globorotalia hirsuta, G. truncatulinoides, G. inflata, G. menardii, Globoquadrina dutertrei, Globigerina pachyderma, Pulleniatina obliquiloculata, Globorotalia crassaformis, Sphaeroidinella dehiscens, and Globorotalia tumida. Selective solution will change the apparent latitudinal origin of a sample toward higher or lower latitudes, depending on the original composition of a sediment assemblage. Solution also will change the aspect of the sample with respect to the original depth habitat of the Foraminifera. This is true especially for morphological variants. Any argument resting on the comparison of living planktonic faunas and their counterparts in the sediment must take these solution effects into account. The selectivity of solution provides a tool with which the relative CaCO3 undersaturation of the ocean water may be measured. In the central Atlantic, the depth at which this undersaturation increases markedly is at about 4,400 m. In the past this depth fluctuated between at least 4,500 and 4,000 m, which reflects the changing thickness of the Antarctic bottom-water layer. Similar studies are possible for the more distant past. The bases for such studies are laboratory experiments establishing the relative solution resistance of the extinct species. End_of_Article - Last_Page 520------------